Can we possibly bump up to 300px wide in the list table? Making the screenshots 300x225. With more details hidden seems like it could help it be more of a visual browsing experience. That change was going to be rolled in with multiple screenshots but 99.9% sure that will be punted.

Always ensure table content clears to the next line. This prevents table content from bunching next to the 'Available Themes' headline, which occurred when only one theme was active on a multisite install.